This invention relates to an improved swivel unit for inflatable packer drill stem test tool assemblies of the type used in testing oil and gas bearing zones.
Drill stem test (DST) tools are mounted in the drill stem or string and are used to evaluate the producing potential or productivity of an oil or gas bearing zone prior to completing a well. Thus, as drilling proceeds, various indications such as core samples may suggest the desirability of testing a certain formation for producing potential. To conduct the test, an inflatable packer and valve assembly is lowered on the drill stem into the uncased well bore to the zone to be tested. The packer is then set by rotation of the drill stem and the valve is opened for flow to the well surface.
The upper end of the DST assembly typically has attached a valve unit and a rigid steel hose through which the sample fluids are conducted. Since the lower portion of the DST assembly must be rotated to inflate the packers while the upper portion of the tool carrying the steel hose must remain stationary, a swivel unit is employed. Prior swivel units were mounted above the packers in the DST assembly and above a tool joint which was used to support the assembly above and below the joint. The usual derrick elevator was secured below the tool joint with the "control head" assembly, which connects the steel hose to the swivel unit, fitting between the elevator and derrick hook. In some situations, especially with smaller hook and elevator arrangements, this produced a cumbersome arrangement as adequate space was not available between the elevator and hook to accommodate the height of the control head. In addition, prior swivel units have had short service lives due to the side loads imposed upon the unit by the steel hose running from the tool to the derrick floor. This off-centered load has caused bearing failure in certain of the previous designs.
There exists a need for a swivel unit which provides adequate space above the derrick elevator and below the derrick hook for the control head which is able to withstand the side loads imposed by the steel hose running to the derrick floor.